Packaging machines are known that integrate the various components necessary to fill and seal a container into a single machine unit. This packaging process, generally stated, includes feeding carton blanks into the machine, sealing the bottom of the cartons, filling the cartons with the desired contents, sealing the tops of the cartons, and then off loading the filled cartons for shipping.
Many packaging machines require one or more linearly driven mechanisms that assist in the various packaging processes. One such mechanism is set forth in U.S. Pat. No. 4,712,665 to McDonald et al. The '665 patent illustrates a container lifting mechanism that includes a vertical tube actuator that is slidably mounted in bearings within a fixed sleeve. A second vertical tube actuator is slidably mounted in bearings within the first vertical tube to have independent vertical movement relative thereto. Vertical linear movement of the carton is accomplished by hydraulic activation of the first and second vertical tube actuators.
Another linearly driven mechanism for use in a packaging machine is set forth in U.S. Pat. No. 4,738,077 to Wakbayashi et al. The '077 patent illustrates an apparatus for forming containers, particularly gable top containers. The apparatus uses a linearly driven fork that pre-folds opposed side panels of the gabled portion of the container. The linear movement mechanism that is used to linearly drive the fork is hydraulically actuated.
In addition to the foregoing hydraulically operated linear actuators, other linear drive mechanisms may be utilized in packaging machines. Such mechanisms include ball screws and linear motors.
Trends within the field of packaging machines point toward increasingly high capacity machines intended for rapid, continuous filling and sealing of a very large number of identical or similar packaging containers, e.g., containers of the type intended for liquid contents such as milk, juice, and the like. The increased throughput and decreased size requirements have increased the demands that are placed on the linear drive mechanisms that are employed. For example, high precision linear movement with little allowable backlash is often desirable and/or required. Likewise, low mass actuators are desirable to facilitate high speed movement of the driven components.
Additional limitations on the linear actuators are imposed by virtue of the hygienic nature of the packaging process. The linear actuators must be designed to limit their contamination of the interior of the packaging machine and, further, must be easily cleaned.